Hyperthyroidism: What causes it, what the symptoms are, how to diagnose and treat it
Hyperthyroidism means the thyroid gland is producing too much thyroid hormone.
What does an overactive thyroid mean?
Hyperthyroidism is a clinical syndrome that develops when the body produces too much thyroid hormone over a long period of time. Thyrotoxicosis is a broader term that also covers situations where the thyroid releases too much hormone (thyroiditis) or where the dose of replacement therapy is too high. The overall prevalence in adults is about 1%, with subclinical forms adding another 1–2%.
Symptoms
Palpitations, a fast or irregular heart rate, weight loss, intolerance to heat and sweating, tremor, anxiety or irritability, sleep disturbances, muscle weakness (in the thighs and upper arms), frequent bowel movements, menstrual irregularities, and warm, moist skin. Eye problems are also a feature of Graves' disease. Older adults may not have as many symptoms. Sometimes they present only with atrial fibrillation, heart failure, or weight loss.
Causes
Graves' disease (most common in young adults), toxic multinodular goiter and toxic adenoma (more common in older patients), thyroiditis (subacute or postpartum, which usually resolve on their own), iodine-induced thyrotoxicosis, excessive exogenous thyroid hormone intake, amiodarone-induced thyrotoxicosis, and rare causes such as TSH-secreting pituitary adenomas, struma ovarii, or metastatic thyroid cancer.
Blood tests
TSH is low (usually below 0.1 mIU/L), while fT4 and fT3 are elevated (overt) or normal (subclinical). TSI/TRAb confirms Graves' disease. If fT3 is high and fT4 is only mildly elevated, this may suggest Graves' disease or an autonomous nodule. Thyroglobulin levels are low in factitious hyperthyroidism caused by levothyroxine intake and elevated in other causes. In subacute thyroiditis, ESR and C-reactive protein levels are high.
Imaging studies
Thyroid ultrasound provides information about thyroid structure: in Graves' disease, a diffuse structural change and intense blood flow are seen. In toxic multinodular goiter there are nodules, in toxic adenoma there is a single nodule, and in subacute (painful) thyroiditis the finding is heterogeneous, hypoechoic, and with low vascularity. When the cause of hyperthyroidism is unclear, the key investigation is pertechnetate scintigraphy. It shows diffuse uptake in Graves' disease, a focal hot area in a toxic nodule, accumulation in different nodules in toxic multinodular goiter, and low or absent uptake in thyroiditis and in cases of exogenous thyroid hormone use.
Treatment
Antithyroid medications (methimazole 10–40 mg per day; propylthiouracil only in the first trimester of pregnancy or in case of methimazole allergy), radioactive iodine therapy, or surgery are used to treat Graves' disease and toxic nodular disease. Radioactive iodine or surgery is usually the best choice for isolated "hot" nodules and for toxic multinodular goiter, because sustained remission with medication alone is rare. Thyrotoxicosis caused by thyroiditis or subacute thyroiditis is transient and is treated symptomatically when needed — with beta-blockers (propranolol or bisoprolol) and, for pain, with NSAIDs or a short course of prednisolone. Untreated hyperthyroidism can lead to atrial fibrillation, osteoporosis, heart failure, or a thyroid storm.
Follow-up and monitoring
Check fT4 and fT3 first every 8–12 weeks and then every 3–4 months while taking thionamides. TSH and TSI take the longest to normalize and are not used to adjust treatment doses. After radioactive iodine therapy or thyroidectomy, check TSH and fT4 every 4–12 weeks until the thyroxine dose has stabilized. After that, check every 12 months. Before starting treatment, patients with subclinical hyperthyroidism (low TSH, normal fT4/fT3) should be retested 2–3 months later. This way, patients with temporarily low TSH who do not need treatment are filtered out.
Medical disclaimer. This article is for general educational purposes and does not replace consultation, diagnosis or treatment by a qualified healthcare professional. Always discuss your individual situation with your own doctor.